Hybrid propulsion systems are coming into common use in motor vehicles. Simple versions of such systems utilize a fuel-based system such as a fuel cell or an internal combustion engine in combination with a storage battery to power the vehicle. In one version of such systems, an internal combustion engine powers the vehicle through a mechanical transmission linkage, and also operates to recharge the battery. The battery, in turn, powers the vehicle through an electric motor, and when the vehicle is in a regenerative braking mode, this motor can operate as a generator to slow the vehicle and recharge the battery. In another version of this system, the internal combustion engine operates in conjunction with a generator to power an electrical motor which drives the vehicle; as in the previously mentioned system, the motor can also charge a battery which also powers the vehicle, and regenerative braking may be incorporated. In either system, the battery itself is capable of propelling the vehicle only for relatively short distances, in the absence of any contribution of power from the fuel-based system.
Plug-in hybrid systems are now coming into use. These systems include a relatively large storage battery which can be connected to an electrical grid when the vehicle is not being driven so as to accumulate charge. The amount of charge stored in the batteries of plug-in systems is relatively large, and typically is capable of propelling the vehicle for distances of over 12 and, in some cases, over 50 miles. Plug-in systems of this type can operate in several modes. In the simple mode, the system first powers the vehicle on solely electrical power until the battery charge is depleted, after which the vehicle is powered solely by a fuel-based system such as an internal combustion engine. In other instances, the plug-in system may operate as a conventional hybrid after the stored power is depleted. In yet other instances, the internal combustion engine may participate, in some degree, in powering the vehicle during the time it is primarily operating on battery power. For example, the engine may be used to provide auxiliary power for passing or hill climbing.
Hybrid vehicle systems of the type described above, which allow for simultaneous vehicle operation under stored battery power and power derived from the oxidation of fuel, include control systems which operate to control both the battery-powered propulsion system and the fuel-based propulsion system, so as to achieve an optimum balance of power and economy. In systems having a relatively small battery for storing electrical power, vehicles primarily are propelled by the fuel-based propulsion system and battery power is utilized to boost the power of the system as needed. In systems having a somewhat larger battery capacity, the controller may operate to allow the vehicle to be driven on solely battery power for longer periods of time, utilizing the fuel-based propulsion system, as necessary, either to achieve extra power, or in those instances when the battery power is becoming depleted. In systems having relatively large storage batteries, such as the plug-in systems described above, the controller may operate to primarily power the vehicle from stored electrical energy, utilizing the fuel-based system as needed for extra power boosts. Once the stored power is depleted to some preselected level, typically 60-80% of battery capacity, the controller may then switch to powering the vehicle primarily from the fuel-based propulsion system.
It should be noted that while this disclosure primarily describes fuel-based propulsion systems as being internal combustion engines, other fuel-based systems, including fuel cells, as well as external combustion engines, may also be used to power the vehicle. Hence, within the context of this disclosure, the hybrid motor vehicle systems are described as including a first propulsion system which is powered by electrical energy stored in a rechargeable battery, and a second propulsion system which is powered by the oxidation of the fuel. This second system can include internal combustion engines, including internal combustion engines which deliver mechanical power to drive the vehicle, and those which power a generator to produce electrical energy, as well as fuel cells which operate to generate an electrical current. Other such combustion-based systems, including turbines, vapor engines and the like, are understood to be included within the definition of combustion-based propulsion systems.
All such hybrid power systems include controllers which operate to achieve a desirable balance of power and economy; and these controllers utilize a program to achieve a desirable blend of electrical and fuel-based propulsion. It has been found that in most instances the operation of a typical non-commercial motor vehicle involves relative small amounts of driving, usually aggregating to less than 50 miles per day, and this mileage is often based upon a number of relatively short trips. However, these same drivers do, on occasion, have need to travel larger distances, hence vehicles must have sufficient range to accommodate longer journeys, which are often unanticipated. In typical hybrid vehicles of the prior art, controllers are operative to achieve a preset balance of power and economy, without talking into account the fact that most trips are relatively short, and daily driving is typically fairly low. As will be described in detail hereinbelow, the present invention factors these driving patterns into the control of a hybrid vehicle system. As such, the present invention “front loads” the electrical power draw on the hybrid propulsion system so that greater amounts of stored electrical power are drawn down in the early operation of the vehicle. Operation in this mode enhances overall fuel economy while preserving the capability of achieving a realistic driving range. These and other advantages of the invention will be apparent in the drawings, discussion and description which follow.